1. Field of the Invention
The present invention relates to the field of optical recording technology and, more specifically, to a SIL (solid immersion lens) near-field flying head flying state control structure.
2. Description of the Related Art
Due to strong market demand for high capacity of optical disks (such as CDs, VCDs, DVDs, and etc.), optical disk manufacturers have not stopped trying to find a method to increase the storage capacity of an optical disk without increasing its size. Currently, there are techniques disclosed to improve optical disk recording density. FIG. 1 illustrates a prior art technique called “near-field recording”, which reduces the size of the laser light spot of the optical flying head 80, so that a relatively thinner signal track can be exposed on the optical disk 90. The optical flying head 80 comprises a slider 81 controlled by a servo to fly above the optical disk 90 at a very low altitude, a semispherical SIL (solid immersion lens) 82 located on the front side of the slider 81, and a focusing lens 83 provided inside the slider 81. The focusing lens 83 focuses the laser beam onto the SIL 82, causing the laser beam to produce a total internal reflection at the front tangent plane 84 of the SIL 82 and, at the same time, an evanescent wave is produced and passed through the front tangent plane 84 of the SIL 82 to expose the optical disk 90.
Because the aforesaid evanescent wave attenuates gradually in index subject to its forwarding distance, the SIL 82 must be precisely controlled in close proximity to the optical disk 90 so that high stability of exposure action can be achieved (remark: normally, the distance between the front tangent plane 84 of the SIL 82 and the photoresist of the optical disk 90 is maintained within 100 nm). The optical flying head 80 shown in FIG. 1 uses aerodynamics to manipulate the flying action of the slider 81 (the so-called “air pad”). According to this method, an outer air passage 86 and an inner air passage 85 are provided in the front side of the slider 81 around the SIL 82, and then compressed air is ejected out of the outer air passage 86 when the inner air passage 85 absorbing air. By means of the aforesaid actions, a constant air gap (about 1 μm) is maintained between the slider 81 and the optical disk 90. Further, an annular piezoelectric material 87 is bonded to the slider 81, forming a lens set. When applying a high voltage to the piezoelectric material 87, the SIL 82 is pushed toward the optical disk 90 to the near-field distance. During working, the amount of total internal reflection is indicative of the distance between the SIL 82 and the optical disk 90 (remark: when the SIL 82 reaching the near-field distance, the amount of total internal reflection is relatively reduced). Therefore, the amount of the high voltage applied to the piezoelectric material 87 is controlled subject to the amount of total internal reflection measured.
However, the aforesaid method can only measure the distance between the center point of the front tangent plane 84 of the SIL 82 and the optical disk 90 for use to control the displacement of the SIL 82 in one axis (the vertical direction in FIG. 1). This method cannot judge the posture of the SIL 82. When the SIL 82 tilted relative to the optical disk 90, the aforesaid prior art mechanism cannot detect and correct the tilted posture of the SIL 82. As indicated above, the aforesaid evanescent wave disperses subject to the change of the distance at a fast speed. Therefore, tilting of the SIL 82 affects near-field exposure quality. Further, because the distance between the SIL 82 and the optical disk 90 is very short, tilting of the SIL 82 may cause the peripheral edge of the front tangent plane 84 to touch the optical disk 90. Therefore, the precision requirement of the aforesaid prior art optical flying head 80 on the parallelism between the lens set and the slider 81 in actual practice is critical (the precision of 1 mrad is the minimum). This precision requirement results in high fabrication difficulty and low product yield rate.